In the electroerosion process referred to, a generic electrode, i.e. an axial or slender electrode tool having an end portion of a generic electrode form, i.e. a simple transverse cross-sectional contour (e.g. circular or square) generally independent of a form to be imparted to a workpiece, is brought into electroerosive machining relationship with the workpiece. The electrode is displaced relative to the workpiece to advance the end portion in a scanning manner or effectively in the workpiece sequentially along successive two-dimensional programmed feed paths, the paths lying in parallel planes which are spaced by a small distance in a third direction, i.e. in the direction of an axis of the electrode tool. An electroerosive machining gap is maintained between the advancing end portion and the workpiece to progressively develop in the latter, a 3D (three-dimensional) machined form corresponding to the successive two-dimensional feed paths as a whole. Conveniently, the 3D-path control is performed by a NC (numerical control) system under programmed path data instructions.
This process has several advantages over the conventional sinking electroerosion process. First, the need to prepare duplicating (complementary) tool electrodes, which must be commonly plural for a single forming operation, is eliminated. Second, a relatively high machining accuracy is obtainable at a relatively high removal rate, viz. even under a "wear" machining condition. Furthermore, the accumulation of discharge products such as removed particles and decomposed gases, an extremely serious problem in the sinking problem, is much less likely to occur, and hence there is less tendency towards short-circuiting, arcing or like abnormal discharge which results in thermal damage to the workpiece or the electrode tool or both.
When, however, such a gap defective condition, which is not completely avoidable in this process as well, happens to develop, the remedy is to extinguish the abnormal discharge and remove the defective condition promptly so that the damage may not occur. This can be achieved partly by terminating the electrical energization in the machining gap by cutting off the supplied machining pulses temporarily but it has been found that this measure is often insufficient to prevent the damage especially where the gap contains a significant amount of the machining detritus which remains unremoved.
Thus, in order to extinguish the arcing condition or short-circuiting not merely temporarily but permanently, it is desirable to expand the machining gap or to move apart the electrode tool and the workpiece temporarily apart so that the accumulated machining detritus can be pumped out of the gap promptly. Thus, it has been suggested to axially retract the electrode tool temporarily away from the workpiece as in the conventional sinking process, to temporarily retract the electrode tool along its preceding path of travel as in the traveling-wire electroerosion process, or to use a combination of such tool retractions. It has been found that none of these modes of tool retractions will necessarily remedy the defective gap condition adequately in the 3D-path controlled generic-electrode electroerosion process.